2013 2(13)

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Pages:

48 - 55

Language:

RU

Ref.:

18


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COMBINATION OF THE METHODS OF IRREVERSIBLE THERMODYNAMICS AND DIFFUSION KINETICS IN CALCULATING THE VELOCITY OF COAL COMBUSTION

Troshenkin B.A.1, Yanko S.V.2, Troshenkin V.B.1

1 A.N.Podgorny Institute for Mechanical Engineering Problems of NAS of Ukraine, Kharkov, Ukraine
2 Academy of Mining Sciences of Ukraine, Branch of Coal, Shale and Peat, Kiev, Ukraine


Citation:

Troshenkin, B.A., Yanko, S.V. and Troshenkin, V.B., (2013) Combination of the methods of irreversible thermodynamics and diffusion kinetics in calculating the velocity of coal combustion, Modern Science: Researches, Ideas, Results, Technologies, Iss. #2(13), PP. 48 - 55.


Keywords:

coal combustion velosity; diffusion kinetics; thermodynamics of irreversible processes; the chemical potential; resistance to burning; heat balance; the analogy of heat and mass transfer


Abstracts:

The purpose of the study - to develop a physically substantiated method of determining the velocity of coal burning. Methodology for achieving of the purpose is to analyzing the known experimental data and compared of the accepted methods of calculation of the coal burning velocity. The study analyzed the advantages and disadvantages of methods of calculating the velocity of coal burning, drawn up on the basis of the theory of diffusion kinetics and thermodynamics of irreversible processes.It is shown that the mathematical representation of velocity of heterogeneous reactions , e.g. coal combustion, as a function of the difference of the concentrations of the oxidant in the stream and on the solid surface is unreasonable. By analogy with the mechanics suggested as the measure of the driving forces of reaction accept the chemical potential, while the factors that hinder the process can be equated to the friction. The resistances of the process are follow: the diffusion of oxidant towards the reaction surface, the absorption of oxidant into crystal lattice and the activation of carbon atoms. In order to keep the balance of the heat inflow and heat removal are recommended to calculate the velocity of the burning in two stages. The first step is to estimate the intensity of heat transfer and by its measure to find the amount of burnout coal at time unit at a concrete location in the furnace section or underground canal. The second step - velocity are calculated depending on the available quantity of the chemical potential with accounting of the resistances of separate stages of the process. Originality are the substitution of the concentrational potential instead of the chemical potential and the putting to the calculation of the velocity of the coal burning the two specificities. Specificity of calculating on the first stage is the consideration of both longitudinal and transverse flow of gases along the burned coal particles or in canal which burned. For this substantiated the size of circulating cells in the boundary layer. The flow velocity of gases which generated in lifting channels of cells calculated according to reducing of the pressure, which in turn, determined by the equilibrium constant and law of mass action. Specificity of calculation on the second stage - the assignment the ratio of the chemical potential not on molar amount of reagents but on the number of atoms in the surface layer, because coal burning take place by layers. After that the kinetic resistance of reaction are calculated by the Arrhenius equation, the adsorptional resistance - select from the reference data, diffusional by the equation relating the mass transfer coefficient with the heat transfer coefficient, which calculated on the previous stage. The practical value is confirmed by achieving universal method and increasing the accuracy of calculations. For a given heat output on the developed method can be defined the capacity of the furnace and the dimensions of the underground heat generator. Taking full account of the process parameters increases the accuracy of the calculations. Calculation of the velocity of combustion are considered to be satisfactory if the difference of balance does not exceed of 10 – 15%.


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